1. Field of the Invention
The present invention relates to a data transmission apparatus, and, more particularly, to a data transmission apparatus of the type transmitting, upon receiving a permission from a higher-level data receiver, a required amount of data to the data receiver, and to a data transmission control method therefor.
2. Description of the Background Art
A data transmission apparatus of the type described transmits data in bursts to a higher-level data receiver connected thereto. More specifically, the data type of transmission apparatus should transmit data in the form of consecutive data sequences, in each of which data not exceeding a preselected unit amount is transmitted. The data transmission apparatus is sometimes required to control the mean amount of data transmitted for a unit period of time to a preselected value. Therefore, circuitry capable of satisfying such different conditions consistently is essential with the data transmission apparatus. This circuitry may generally be configured to establish a reference threshold, below which an amount of data is controlled to be transmitted for a unit period of time.
In practice, however, the data transmission apparatus cannot easily absorb, condition by condition, an error or difference between an amount of data actually output and an expected control value by simply executing control with an invariable value. The apparatus cannot achieve accuracy satisfying the conditions described above unless it absorbs such an error. Moreover, the errors are dependent upon a unit amount and a mean amount of data to be transmitted, which are conditioned from the outside of the apparatus. Specifically, the error increases with an increase in the unit amount of data and with a decrease in the mean amount of data, lowering the expected value of data transmission.